With increasing participation in athletic activities, knee ligament injuries have become more common. Those wishing to participate in athletic endeavors after an injury often use a brace to protect the damaged knee from reinjury. Optimally, the brace will prevent the injured knee from orienting itself in a "subluxed" position, wherein the relation between the tibia and the femur has become skewed away from an anatomically sound or "conjugated" position.
The knee reaches a critical period during the transition from an "unloaded" or "lowload" state (wherein the knee is not supporting any weight) to a "loaded" state (wherein the knee is supporting the body's weight). In order to prevent injury, the tibia and femur must be in a conjugated position at the time of loading. If the knee joint is in a subluxed position at loading, a reflex proprioceptive arc unconsciously causes a reflex inhibition of muscle function, thereby reducing support to the leg and resulting in disabling "giving way" symptoms that occur with unstable knees. Whereas subluxation of the tibia often occurs while the knee is in an unloaded state, it seldom occurs once the knee has become loaded in an anatomically stable position. Hence, the primary function of a brace should be to prevent subluxation while the knee is in an unloaded state.
During flexion and extension of the leg, the tibia rotates about an axis generally parallel to the medial side of the tibia. In the normal rotational mechanics of the knee, the tibia undergoes a progressive external rotation as the knee is brought through the last thirty to forty degrees of extension. This allows for the so-called "screw home" mechanism to occur as the knee reaches terminal extension. During this phase, the rotation of the tibia is most important, since the tibia must reach its proper conjugated position before loading.
Two types of braces have heretofore been available to prevent subluxation of the knee. The first type of brace is a "rigid" brace, in which a rigid thigh piece is linked to a rigid tibial piece by two rigid hinges. Rigid braces attempt to prevent tibial subluxation at full extension by preventing any rotation of the tibia during flexion or extension. Due to the inability to rigidly grasp the involved extremity, some degree of rotation may occur either by the brace shifting on the skin or by the skin envelope shifting around the involved leg. While the rigidity imparted by this type of brace increases the resistance to subluxation of the tibia at terminal extension, it also resists the normal rotations that need to occur during functional activity.
The second type of brace rotates the tibia in a set arc, or degree of motion, during flexion and extension. While these braces allow rotation of the tibia, a predefined path of motion must be set at the factory based on data supplied by the user's physician. Consequently, adjustments to the rotating mechanisms of these braces must also be made at the factory, resulting in inconvenience and expense to the user. Furthermore, these braces have a low margin of error, i.e., if the brace is not perfectly positioned on the user's knee, the tibia will not follow its normal path, and subluxation will result.
Therefore, a need has arisen for a knee brace which allows free rotation of the tibia, yet positions the knee in an anatomically stable position prior to loading. Furthermore, a need exists for a knee brace whose range of rotation may be easily and accurately adjusted by the user or by a qualified physician.